142 THE CRAYFISH 



an injected specimen, and will be described later 



(p. 151). 

 i. From the anterior end of the heart arise a median 

 ophthalmic artery and a pair of antennary 

 arteries ; and behind and below these a pair 

 of hepatic arteries, 

 ii. From the hinder end of the heart arises the large 

 median dorsal abdominal artery, and imme- 

 diately below this the large median sternal 

 artery, which latter can be better seen at a 

 later stage. 



d. The alse cordis are three pairs of fibrous bands 

 which hold the heart in position by connecting it 

 with the walls of the pericardial sinus. 



Bemove the branchiostegite and turn down the gills of the 

 left side, unless this has already been done. 



2. The branchioeardiac canals are a series of channels in 

 the body-wall, conveying blood from the gills to the 

 pericardial sinus. They can be seen through the 

 transparent body-wall running from the bases of 

 the gills, and converging to open into the sides of 

 the pericardial sinus. 



Gut a gill off close to its base, and blow into the cut end 

 ^of the efferent blood-vessel with a blowpipe, or inject some 

 ■coloured fluid into it, and observe the air or coloured flvM, 

 ■entering the pericardial sinus. 



;B. The Reproductive System. 



Carefully remove the side-wall of the thorax, and expose 

 ■ihe reproductive organs. 

 a. In the male. 



i. The testis is a soft white body lying immediately 

 below the pericardial sinus, and extending 

 backwards a little beyond it. It consists 

 of a pair of anterior lobes, and a median 

 posterior lobe. 



